Differently colored lights have been used as indicators for a very long time. Sometimes, colors indicate absolute or relative position, such as that a viewer is in a “dangerous” as opposed to a “safe” sector. Every nighttime driver knows the difference between red tail lights and white headlights.
As another example, in 1848 the United Kingdom began requiring certain ships to display red and green navigation sidelights on their port and starboard sides, respectively; this rule was adopted internationally in 1898. Nowadays, the International Regulations for Preventing Collisions at Sea 1972 (COLREGS) published by the International Maritime Organization (IMO) specify which lights of which colors may/must be displayed by vessels of different types, lengths, etc. For most categories, for example, a vessel underway from sunset to sunrise must display a red sidelight whose light is visible from straight ahead (0°) to 22.5° abaft the starboard beam, that is, 112.5° arc, a green sidelight visible from 0° to 22.5° abaft the port beam, and a white stern light visible over the remaining 135° arc centered on the stern.
As for visibility, COLREGS, Part C (“Lights and Shapes”), Rule 22 (“Visibility of Lights”) (b), specifies, for example, the following minimum visibility ranges for navigational lights for vessels of 12 meters or more in length but less than 50 meters in length:                a masthead light, 5 nautical miles (nm), except that where the length of the vessel is less than 20 meters, 3 nm;        a sidelight, 2 nm;        a sternlight, 2 nm; a towing light, 2 nm;        a white, red, green or yellow all-round light, 2 nm.        
For the sake of compactness, wiring simplicity, etc., especially smaller vessels often use lights that combine two or more colors in a single fixture. For example, a single red/green light can be mounted on the centerline at the bow of the boat, or a sailboat less than 20 m in length may have a tri-color light at the top of the mast.
FIG. 1 illustrates a dual-color light fixture 10 as is found mounted on the bow pulpit of many power and sailboats: A casing 15 includes a rear mounting plate 20 that has some kind of mount or bracket 22 and is often joined with top and bottom plates 30, 32. A translucent lens member 40, most commonly made of plastic such as polycarbonate, or high-impact glass, extends in an arc from either side of the rear mounting plate 20 and between the top and bottom plates 30, 32. The angular range of the translucent lens member 40 is typically about 2*(90+22.5)°=225° to meet the COLREGS visibility requirements.
In known lights of the type shown in FIGS. 1-3 an incandescent bulb 50 is mounted in a fitting 52 to serve as the light source. A cap 60 or knob or the like allows an electrical cable 70 to reach the fitting 52 and typically seals the bottom of the lamp so that it is water-proof.
FIGS. 2 and 3 illustrate how known lamps create different light colors in different sectors. As illustrated, the translucent lens member 40 comprises different portions, one for each desired light color. In the illustrated example, these are a red portion 40R and a green portion 400. The light source 50 typically creates light with a broad spectrum (as close as possible to “white,” indicated in the figure by “W”) that includes substantial energy at red and green wavelengths for the required visibility at the specified distance. Since the colored translucent lens portions 40R, 400 act as filters, as viewed from the port side the light 10 will shine red and as viewed from the starboard side the light 10 will shine green.
Of course, the translucent lens member 40 may be divided into more than two portions, and different colors may be used besides red and green. In a masthead tri-color light, for example, the translucent lens will extend essentially 360°, with a clear portion 40W (FIG. 3) facing aft so as to create the required white stern light. Moreover, the translucent lens member 40 is often not smooth or necessarily uniformly thick, but rather may have ridges or frosting or other features so as, for example, to create a lens effect to aid in focusing and aiming the light and improving its visibility within certain vertical and or horizontal planes.
As mentioned, each colored portion 40R, 400 of the translucent lens 40 acts as a filter to pass the respective intended color (that is, range of wavelength) of light from the source 50. This makes it possible to use a single light source 50 (one or maybe even more bulbs or other light-emitting elements) yet still have light of different desired colors from a single light, but it also carries a clear disadvantage: To filter out unwanted wavelengths also means to reduce the intensity of the light that otherwise would pass through the translucent lens 40.
As a result, given known lights of the type illustrated in FIGS. 1-3 with typical lens 40 thicknesses, materials, surfaces, etc., to achieve the 2 nm visibility required by the COLREGS, the light source 50 usually needs to be at least 10 Watts incandescent for “white” light through a substantially non-colored or clear lens portion, and at least 25 Watts incandescent for red and green. If a single white light source 50 is used for all sectors/lens portions, then this means that at least 25 W incandescent is required. By way of example, if one were to run such a light for even ten hours during a night passage on a recreational boat with a standard 12V dc electrical system, then this would drain at least (25/12)10=21 Ampere-hours from the battery bank, which is a significant drain for only one light.
FIG. 4 shows one known way to reduce the effect of this disadvantage: Instead of a single-color light source 50, a light source 90 is included in the form of an arrangement of individual LEDs such that red LEDs aim out through the red portion 40R of the lens 40 and green LEDs aim out through the green portion 400. One disadvantage of this arrangement is that correct mounting of the many LEDs on some substrate such as PCB material complicates the manufacturing process—each LED will require two solder joints, one for each electrode, and also must be correctly aligned so as to shine in the intended direction. Moreover, the substrate often has a complicated shape, such as being cylindrical or different planes, etc. To prevent misdirection and waste of light, each group of LEDs may also be provided with—usually mounted within—a dedicated backing reflector (analogous to a standard flashlight or car headlight reflector) that aims their light according to a desired pattern; this further complicates the manufacturing process.
What is needed is a light that reduces or eliminates some or all of the shortcomings of existing multi-color indicator lighting.